Swift学习之控制语句

October 7, 2015 6 分钟阅读

for-in循环
for循环
while循环
repeat-while循环
if判断语句
switch语句
控制转移语句

for-in循环

1.for-in循环可以遍历的对象：区间、数组（Array）、字典（Dictionary）、集合（Set）

for index in 1...5 {
  println("\(index) times 5 is \(index * 5)")
}

2.如果不需要每一项的值，可以用_替代

for _ in 1...5{
  println("hello, five times")
}

for循环

可以按照C语言理解，例子的index仅循环内有效，除非循环外定义。

for var index = 0; index < 3; ++index {
  print("index is \(index)")
}

while循环

可以按照C语言理解

var index = 0;
while index < 3 {
  printf("index is \(index)");index++
}

repeat-while循环

可以按照C语言do-while循环理解

var index = 0;
repeat{
  printf("index is \(index)");index++
}while index < 3

if判断语句

可以按照C语言理解，更多判断用if…else if…else

var temperatureInFahrenheit = 30
if temperatureInFahrenheit <= 32 {
  print("It's very cold. Consider wearing a scarf.")
}

switch语句

1.类似C语言，switch…{case value1:…case value2:…default:…} ;不能贯穿，不同于C语言用break防止贯穿；case分支必须至少有一条语句，哪怕是break语句； case语句可以包含多个模式，用,隔开,如case value1,value2:。举例如下：

let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a","A":
  print("The letter A")
default:
  print("Not the letter A")
}

2.case语句可以是区间

let approximateCount = 62
switch approximateCount {
case 0:
  println("no")
case 1..<5:
  println("a few")
case 5..<100:
  println("several")
default:
  println("many")
}

3.switch可以判断元组，且可以用_表默认

let point = (1, 1)
switch point {
case (0, 0):
  print("(0, 0) is at the origin")
case (_, 0):
  print("(\(point.0), 0) is on the x-axis")
case (0, _):
  print("(0, \(point.1)) is on the y-axis")
case (-2...2, -2...2):
  print("(\(point.0),\(point.1)) is inside the box")
default:
  print("(\(point.0),\(point.1)) is outside of the box")
}

4.可以用let只绑定

let anotherPoint = (2, 0)
switch anotherPoint {
case (let x, 0):
  print("on the x-axis with an x value of \(x)")
case (0, let y):
  print("on the y-axis with a y value of \(y)")
case let (x, y):
  print("somewhere else at (\(x), \(y))")
}

5.case语句可以接where进行额外判断

let yetAnotherPoint = (1, -1)
switch yetAnotherPoint {
case let (x, y) where x == y:
  print("(\(x),\(y)) is on x == y")
case let (x, y) where x == -y:
  print("(\(x),\(y)) is on x == -y")
case let (x, y):
  print("(\(x),\(y)) is some arbitrary point")
}

控制转移语句

1.continue和break按照C语言理解 2.fallthrough用于switch中贯穿 3.循环或switch前，可以用上标签，方便用continue和break明确继续或终止的循环对象

gameLoop: while square != finalSquare {
  if ++diceRoll == 7 { diceRoll = 1 }
  switch square + diceRoll {
  case finalSquare:
    // 到达最后⼀个⽅块，游戏结束
    break gameLoop
  case let newSquare where newSquare > finalSquare:
    // 超出最后⼀个⽅块，再掷⼀次骰⼦
    continue gameLoop
  default:
    // 本次移动有效
    square += diceRoll
    square += board[square]
  }
}
print("Game over!")

HarmonyHu